Power supply apparatus for alternately supplying a load



Oct 1953 v. T. CALLAHAN ET AL 2,655,603

POWER SUPPLY APPARATUS FOR ALTERNATELY SUPPLYING A LOAD Filed Aug. 14,1952 s Sheets-Sheet 1 FIG.

ATKTORNEY Oct. 13, 1953 v H N ETAL 2,655,603

POWER SUPPLY APPARATUS FOR ALTERNATEILY SUPPLYING A LOAD Filed Aug. 14,1952 3 Sheets-Sheet 2 v t CALLAHAN //VVE/VTOR$ A TTOR/VE Y 1953 v. T.CALLAHAN ET AL POWER SUPPLY APPARATUS FOR 2,655,603 ALTERNATELYSUPPLYING A LOAD 5 Shuts-Sheet 3 Filed Aug. 14, 1952 WIR l l l![CALLAHAN L. 0. FR)

ATTORNEY Patented Oct. 13, 1953 UNITED STATES PATENT OFFICE POWER SUPPLYAPPARATUS FOR ALTER- NATELY SUPPLYING A LOAD Application August 14,1952, Serial No. 304,316-

6 Claims.

This invention relates to power supply apparatus and particularly tosuch apparatus for supplying current to a load from two enginedrivengenerators during alternate time periods.

In a specific embodiment. of the invention herein shown and describedfor the purpose of illustration, there are provided two engine-drivengenerator sets for alternately supplying current to a load. When a firstof the generators, for example, hes been supplying current to. the loadfor a predetermined period, a motor-driven cam switchcloses afirst/circuit for controlling the starting of the engine for driving thegenerator of the second engine-driven generator set. If the. secondengine-driven generator starts, the first generator continues to supplycurrent to the load dlll'illga period in which the output voltage of thesecond generator builds up. When the output voltage of the secondgenerator has increased to a predetermined value, relay means areenergized for controlling the energization of a transfer switch, after adelay period, and the transfer switch operates to. transfer the loadfrom the first generator to the second generator. If the output voltageof the second generator remains at a sufficiently high value when the.load is transferred to the. second. generator, means are provided forshutting down the first enginedriven generator- When the secondgenerator has been supplying a current to. the load for a predeterminedtime period, the cam switch closes a second circuit forccntrollingthe.starting of the first engine-driven generator, the firstcircuit having previously seen opened by the cam. switch. When theoutput voltage of the first generator reaches a certain operating value,the transfer switch is again operated, after a delay period, and theload is tranferred from the second generator to the first generator.Subsequently the, second enginedriven generator is shut down.

Under certain abnormal operating conditions, a generator which issupplying'current to the load may be shut down prior to the expirationof its normal operating period. In this case the second engine-drivengenerator is started and, when its output voltage reaches an operatingvalue, the transfer switch is operated with a minimum delay to transferthe load to the second generator. In order to restart the firstgenerator after the cause of its failure has been corrected, it isnecessary to reset certain relays manually. If, after one of theengine-driven generators has been started and the load has beentransferred to it, the generator output voltage should drop 2 below avpredetermined value, means are provided for preventing the stopping ofthe second enginedriven. generator and the,- loed is transferred back tothe; second generator.

Each of the engine-driven generator sets which alternately supplycurrent to the load isv provided with motor operated. air recirculatinglouvers, the motor and. its controller being connected across the loadthrough fuses. Relay means are provided for operating an alarm when oneof the fuses, blows and for blocking the operation of the alarm in respnse to, failure of load voltag while one of the generatorsis operatingto produce an output voltage. However, .ere is pro.- vided: a secondalarm which is operated. in response to. load voltage failure. Relaymeans are also provided for causin the operation of the first mentioned,alarm in the, event that both generators fail to. produce outputvoltage, the second alarm also being operated for this condition due tofailure of voltage across the load.

Figs. 1, 2 and 3, when. placed with res; set to each other as shown inthe diagram of is. 4. are a schematic View of a power supply apparatusembodying the invention.

Referring to the drawing: there are provided for supplying alternatingcurrent to a load I6 durin alternate'time periods two similar dieselengine driven, three phase alternators. One of the alternators Iiidrivenv by a diesel engine I I and controlapparatus therefor are shownwithin the dash line enclosure M. The apparatus included within a box Itis. the same as that provided within theenclosure It, and includes thesecond alternator lZ-driven by a diesel engine It. The apparatus isdesigned so that one of the engines will run for a desired period, saytwelve hours, and then the other engine will run fora. desired period ofsay twelve hours, etc.

One of the output terminals of each of the alternator-s l0 and i2, andoneof the load terminals are connected to ground. The remainin outputterminals of the alternators, respectively, are connected to the load itthrough contacts of. a transfer switch TS. With. the switch TS in thepositionshown in the drawing, output terminal ll of alternator it isconnected by way Tithrough armature I of transfer switch TS to line Llgoin to terminal 2| of load is. Output terminal [8 of alternator, it isconnected by way of line T2, through armature 2 of transfer switch TS toline L2 oing to, a terminal 22 of load iii. When transfer switch TS isenergized, output terminal IQ of alternator i2 is connected by way oflead 2T4 through. armature l of transfer switch TS to line Li going toload terminal 2i and output terminal 25 of alternator $2 is connected byway of lead 2T2 to armature 2 of transfer switch TS to line L2 going toload terminal 22. The switch TS is of the type in which a sh: ftcarrying the switch armatures i, 2, 3 and 4 is rotated alternately inopposite directions in response to successive pulses of energy suppliedto the electromagnet of the switch. Therefore, when the switch TS issubsequently again energized the switch armatures i, 2, 3 and 4 will bemoved back to the position shown in the drawing to reconnect the load toalternator [9.

There is provided a cycle timer CT comprising a motor 23 for driving thecams 24 and 25 at a rate such that the cams make a complete revolutionin twenty-four hours for example, contacts 2 and 4 of the cycle timer CTbeing closed alternately. One terminal of motor 23 is grounded and theother terminal is connected to lead LIF and thence through a use 56 toline Ll going to load terminal 2 l, thereby energizing the motor.

The apparatus and its operation will be further described assuming thatdiesel engine II is about to complete twelve hours of operation. Itshould be noted that contact 4 of cycl timer CT opened about one-halfhour after the starting of engine II and that relay iCL remainedenergized, after the opening of contact 4 of CT, by current suppliedover a circuit from line LI, line LIF, contact iii of relay 2CL contact3 of relay ICL, winding of iCL, line LZF, fuse 54 to line L2, LI and L2being connected to load terminals 2| and 22, respectively. When contact2 or" the timer CT closes, relay ZCL is energized due to the completionof a circuit traced from line Ll through line LIP, contact 2 of timerCT, the winding of relay 2CL and line LZF to line L2. Contact IQ ofrelay ZCL opens due to the operation of relay ZCL to cause relay lCL torelease, and contact 3 of relay ZCL closes to lock up relay 20L. Therelease of relay iCL completes a circuit from output terminal [9 ofalternator l2 through lead 2Tl, reactor 27, condenser 28, rheostat 29,winding of power failure relay EPF, contact 5 of relay ICL and lead 2T2to input terminal 20 of generator i2, thereby completing an energizingcircuit for relay ZPF when alternator 12 is driven by the engine i3.Operation of relay 2CL opens its contact 9 to open a circuit comprisinglin T2, contact 9 of relay 2CL, winding of power failure relay lPF,rheostat 3G, condenser 3| and reactor 32 to line Tl, thereby releasingrelay IPF. Release of relay {PF opens at its contact the circuit fromline T2 through contact 9 of relay 2CL, the contact of relay lPF, thecontact 3 and the winding of transfer relay lTR to line Tl, therebyreleasing relay ETR.

Four circuits are affected by the release of relay lTR. Contact 3 ofrelay lTR opens to remove the lock-up path for that relay. Contact 9 ofrelay iTR closes to prepare a circuit for transfer switch TS so that itwill operate when transfer switch control relay ETSC operates at the endof the operation of the hold-over timer IHOT, contact '5, and thewarm-up timer ZWUT, contact 8. The energizing circuit for transferswitch TS may be traced from line 2Tl, contact 9 of relay ITR, thecontact of relay ZTSC, armature l of transfer switch TS, the winding ofswitch TS and armature 3 of switch TS to line 2T2. Contact ll] of relay[TR closes and prepares the circuit to hold-over timer ZHOT when engine13 is operating and engine H is Warming up for the next operatingperiod. Contact ll of relay ITR closes to complete a circuit fromnegative battery through fuse 36, contact I I of relay ITR, winding ofmain control relay ZMC, contact 8 of overcranking relay 20C, contact 5of low oil pressure and high water temperature relay ZLOHW, contact 4 ofover-speed trip relay 20S, lead PX2 to apparatus l5 and over-load timer0LT to ground, thereby operating relay ZMC.

With the main control relay 2MC operated, contact 5 thereof opens sothat relay iTR will not operate immediately upon return of power fromgenerator l9. Contact 3 of relay 2MC closes to complete a circuit fromground through contact 3 of relay 2MC, winding of pilot relay 2P,contact ll of relay ITR and fuse 36 to negative battery, therebyoperating relay 2P. Contact I of relay 2MC closes to complete a circuitfrom negative battery, through fuse 35, contact 1 of 2MC, lead PI ofapparatus l5 and relay Pl to ground, thereby operating relay PI ofapparatus 15 which is the control relay for the engine air shut-downcircuit.

The operation of pilot relay 2P aiiects two circuits. Contacts 3 ofrelay 2P close to complete a circuit from negative battery throughcontacts 3 of relay 2P, lead THS to apparatus l5, winding of relay ASDIand contact of thermal relay ASDT of apparatus 1 5 to ground. Relay ASDloperates and locks up through its contact 3. Operation of relay ASDIprepares, through its contact 6, an energizing circuit for operating theair shut-down valve ASD for engine l3 if relay Pl releases because ofintentional shutdown or trouble shutdown. Contacts '2 of relay 2P closeto apply negative battery through contact 4 of relay 20C, contact 2 ofrelay 2P, contact 6- of relay ZAP, lead CO4 going to apparatus l5,contact of cranking cut-out relay CCO, emergency switch ESW and windingof starting contactors t ground, thereby operating the startingcontactor ST. Operation of contactor ST completes a circuit foroperating starting motor M for cranking the diesel engine it. After theengine fires and reaches a speed of seven hundred to eight hundredrevolutions per minute, the contacts of cranking cut-out switch CO5close to cause the cranking cut-out relay CS0 to operate, therebyopening the energizing circuit for starting relay ST causing it torelease. The relay CO0 is operated all of the time that the engine isrunning.

After engine if. has started and is driving the alternator l2, engine llcontinues to drive alternator l2": for a subsequent period and theoutput of alternator l6 continues to supply current to the load. Whenthe output voltage of alternator l2 builds up to about 94 per cent ofnormal voltage, power failure relay EPF and alternator potential relay2A? ar energized by way of leads ET! and 2T2 to cause the operation ofthese relays. Operation of relay 2AP opens at its contact 6 theenergizing circuit for starting contactor ST. The closin of contact 8 ofrelay ZAP completes, through contact 9 of relay lTR, a circuit forsupplying current from alternator [2 over leads 2T! and 2T2 to warm-uptimer ZWUT causing its motor M to run and its clutch to engage to drivethe cams ii! and 38. When relay 2WUT has operated for about four andone-quarter minutes, its contact 8 closes to prepare a partialenergizing circuit for relay ETSC comprising lead 2T], contact 9 ofrelay lTR, winding of relay ZTSC, resistor 39, condenser 46, opencontact I of holdover timer lI-IOT, contact 8 of timer 2WUT to lead 2T2,this circuit being completed when contact I. of timer IHOT closes,aswill be described below.

When power failure relay 2PF operates, it completes a circuit from leadZTI to hold-over timer IHOT, contact of relay 2TB, contact of relay EPFand contact 9 of relay ICL to lead 2T2 to cause the operation of timerIHOT. The clutch of the timer engages and its motor It drives the cams Hand .2. i he hold-over timer has a four and three-quarter minutecontrol, contact 8. operated by cam GI, set to prevent stopping ofengine II in case the operation of engine-alternator I 2, I3 is notsatisfactory to assume the load. It also has a four and one-half minutecontrol, contact 1 operated by cam 42, to permit transferring the loadfrom alternator ID to alternator I2.

The closing of contact I of timer 'IHOT completes a circuit from lead2T2 through contact 8 of timer ZWUT, contact I of IHOT, condenser 40,resistor 39, winding of relay 2TSC, contact 9. of relay I'IR to leadITI, causing relay ZTSC to operate. A circuit is thus completed fromlead 2TI through contact 9 of relay ITR, contact of relay ZTSC, armature4' of transfer switch TS, the winding of TS, armature 3 of TS to lead2T2. The transfer switch TS is thus operated to transfer the load fromalternator ID to alternator I2.

When contact 8 of timer iHOT closes, a circuit is completed from lead2T2 through contact 5% of relay IOL, contact of relay 2P3, contact 8 oftimer IHOT, winding of relay 2TB to lead 2TI, thereby operating transferrelay 2TB. Relay 2TH locks up through its contact 3 and the con-- tactof relay 2P3. The energizing circuit for timer IHOT is opened at contactN3 of relay ZTR to release timer IHOT. The opening of contact 9 of relay2TH, opens the circuit through the contact of relay ITSC going to acontact and armature 4 of transfer switch TS, thus leaving switch TSready to be operated to transfer the load from alternator I2 toalternator Ill at the end of the twelve hour period of operation ofalternator I2, or in the event that alternator l2 fails during thetwelve hour operating period. The opening of contact I I of relay 2TBopens the energizing circuit for main control relay MC to cause it torelease.

Release of relay IMC opens the circuit from negative battery throughcontact I of relay iMC, lead PI, winding of relay PI of apparatus [4 toground, causing relay PI to release. A circuit is thus completed fromnegative battery through lead B, contact of relay Pl, contact 6 of relayASDI and air shut-down valve ASD to ground, thereby operating the airshut-down valve A82") to stop engine H. The energizing circuit for pilotrelay IP is opened at contact 3. of relay IMC and at contact II of relayRelease of relay IP opens at its contact 3 the energizing circuit forrelay ASDI of apparatus Hi. The cir cuit for operating start relay ST ofapparatus 14 is opened at contacts 2 of relay IP. The ASDT timeroperates to release ASDI and after it cools, the circuit is thenrestored to normal with engine alternator Iii, II ready to take over theload at the end of a twelve hour operating period of engine-alternatorI2, I3 or if the engine alternator I2, I3 should fail for any reason.

The operation of restarting the engine-alternator I U, I I and thetransfer of the load from alternator I2 to alternator I6 is similar tothat d scribed above for starting engine I3 and for transferring theload from alternator in to alternator I2. Stated briefly, when contact 4of cycle 6 timer CT closes, relay ICL is energized to. cause itsoperation and to cause relay 20L to releaserelays ZPF and 2TB. RelaysIMO and IP are operated to cause the operation of relay PI and startrelay ST of apparatus Id. The engine II is thus started to cause it todrive alternator IE and when its voltage builds up, relays MP and IPFoperate. Warm-up timer IWUT and hold-over timer ZHOT are energized andrelay ITSC is operated. A resistor I8 and a condenser II are provided incircuit with the winding of relay ITSC as are the resistor 35} andcondenser c in circuit with the winding of relay 2TSC to prevent relayoperation if both frequency and voltage are not correct. The transferrelay TS is energized to transfer the load from alternator I2 toalternator Hi.

When either engine-alternator Ill, H or enginealternator I2, I3, wvhilecarrying the load is shut down due to low oil pressure, high watertemperature or over speeding, as will be described below, the associatedpower failure relay PF, the cycle-timer relay CL and the warm-up timershort circuiting relay WUTS are released. As,- sume, for example, thatengine alternator id, H is carrying the load and that it is shut downdue to one of the above causes, power failure relay iPF, cycle-timerrelay I CL and warm-up timer short-circuiting relay W UTS are released.When relay IPF releases, its contact opens to cause transfer relay ITP.to release. Contact I i of relay ITR closes to cause relay ZMC tooperate and the operation of relay 2M0 completes a circuit causing relay2? to: operate. The engine i3 is thus caused to start as previouslydescribed. Then power failure relay ZPF and alternator potential relay2AP are operated, as described above. As soon as the output voltage ofalternattor I2 builds up to the required voltage, warm up timer ZWUTstarts to operate and at the endof a period of fifteen to twenty-fiveseconds transfer switch control relay ZTSC is o because of thecompletion of energisi g cir cuit fromv lead 2T2, through contact i oftimer ZWUT, contact 6 of. relay W'U'TS, condenser, 49, resistor 39,winding of relay contact 9 of relay lTR to lead flTi. operates, itscontact closes to complete for supplying from alternator 2 to tra 1switch TS, causing it to operate, and transfer the load to alternatori2. Alternator l2 will then carry the load until the trouble conditionon ongins-alternator ii been corrected.

If the engine lubricating oil pressure drops too low or if the enginecooling liquid temperature becomes too high, the engine it or i3 isstopped automatically. When the lubricating oil pressure for engine I I,for example, rises to pounds per square inch, the contacts of the lowoil pr sure switch LOPS open. When the fuel oil rises to 6 pounds persquare the contacts of fuel oil pressure switch close. opening ofcontacts LOPS and the closing of contacts FPS prepare the protectivecircuits to shut the engine down in case LOYPS closes becauselubricating oil pressure drops below 16 pound per square inch, or incase high water temperature switch HWTS closes because the cooling liqud temperature reaches a certain abnormally r" value. To prevent falseoperation of l J oil pressure switch shutdown during the startingperiod,if the fuel oil pressure should build sufliciently to close the fuel oilpressure switch contacts before the contacts of LOP-S open, the oilpressure delay thermal relay OPD is provided.

If the fuel oil pressure switch FPS contacts and the contacts of LOPSare closed at the same time for a period of twenty to thirty-fiveseconds, the CPD heater closes the OPD contacts and relay LOP isoperated. When relay LOP operates, or when the contacts of HWTS close, acircuit is completed from negative battery through the contacts ofl-IWTS or through the contacts of relay LOP, lead LOHW and winding ofrelay iLOHW to ground, thereby causing relay LOI-IW to operate and tolock up through its contact 5. Contact 5 relay ELOHW opens to releaserelay lMC to cause the engine H to stop. Engine 53 will then be startedas described above, and current will be supplied to the load fromalternator l2. The cycle timer will continue to operate and contact 1will subsequently close. Relay lCL will operate and relay ZCL willrelease. When contact 9 of lCL opens, power failure relay 2P1 releasesand transfer relay 2TB releases. Contact H of 2TB closes but maincontrol relay iMC cannot operate to start engine ll because contact 5 ofrelay iLOHW is open. Therefore, engine :1 cannot be started and the loadwill continue to be supplied from alternator If the starting motorcurrent is excessive such as would occur if the engine bearings seize,th -rmal relay LT operates to open the enei circuit for relay IMC or2M9, causing relay or to release to open the starting circuit by openingcontacts 2 of the IP or '2? relay and the motor M of apparatus 14 orapparatus 25 cannot crank the engine it or the engine 22 until the relay0LT is reset manually. The alternator which is carrying the load willcon inue to do so.

When relay 1? operates to complete a circuit for operating the startingrelay ST of apparatus l4 for example, a circuit is also closed fromnegative battery through contact 4 of over-cranking relay lOC, contacts2 of relay IP, contact 6 of relay lAP, lead CO4, contacts of relay CCO,contacts of switch ESW, lead CO and the heater of thermal sw' ch CRT toground, thereby operating relay lCRT to cause it to close its contactsafter a delay period of about thirty-five seconds if the engine has notstarted in that time. Belay lOC is thus energized to cause it to open atits contact 4 the energizing circuit for starting contactor ST and, atits contact 8 the energizing circuit for relay IMC. Subsequently, theengine cannot be cranked until the relay [CRT is reset by hand.

When the engine speed reaches 1360 to 1430 revolutions per minute, theover-speed trip switch 0ST closes its contacts to complete an energizingcircuit for causing the operation of relay 0ST! of apparatus M, forexample. A circuit is thus completed from negative battery throughcontact of relay OSTI, lead 0ST, winding of over-speed trip relay IOST,lead PX2 and relay OLT to ground, thereby causing relay IOST to operateand lock up through its contact 4. Closin of contact 5 of relay IOSTcompletes an energizing circuit for relay IOS. Contact 6 of relay SOS isclosed to energize an alarm circuit 83. Contact 4 of relay IOS opens tointerrupt the energizing circuit for relay IMC, thereby stopping theengine II. To subsequently sta t engine it it is necessary to manuallyreset the relay lOST. If any of the battery fuses of apparatus M or E5,or if either of the discharge fuses 3E blows, an energizing circuit iscompleted for operating the IOST or the ZOST relay to stop the engine IIor 13 respectively.

There are provided a motor 58 for operating air recirculating louver forengine H and a motor 60 for operating air recirculating louver forengine [3, the circuits for energizing motors 58 and 60 being completedby controllers 59 and 6|, respectively. Whether these louvers are openor shut depends upon the position of the controller Which, in turn,depends upon the room temperature. When the controller 59 is in aposition to complete an energizing circuit for motor 58, current issupplied from alternator 10 to a circuit comprising lead Tl, lead Ll,fuse 55, lead 5|, controller 59, motor 58, lead 50, fuse 54, line L2 andline T2. Similarly, when the controller Si is in a position to completean energizing circuit for motor 60, current is supplied from alternatorl2 to a circuit comprising lead ZTI, lead Ll, fuse 57, lead 53, motor6!], controller 6|, lead 52, fuse 55, line L2 and line 2T2.

If fuse 54 or 56 should blow, relay IFAI is released. If relay IPA isoperated, the release of relay IFAI completes a circuit from groundthrough a contact of relay IFA, winding of thermal relay IFAD, resistor62 to negative battery. After a delay period of 1.5 to 2.5 minutes,relay lFAD operates to complete a circuit for energizing relay IOST.Operation of relay IOST completes a circuit for causing relay IOS tooperate, thereby completing a circuit for energizing the alarm 63. Ifrelay IFA should be released, however, due to no voltage across line Ll,L2 going to the load, the relay IFAD will not be energized and the alarm63 will not be energized. Similarly, if use 55 or 5! should blow acircuit is completed for energizing the alarm 83, relay ZFAD beingenergized through a circuit comprising a resistor 83, heater of ZFAD andcontacts of relays EPA and 2FAI.

In the event that neither alternator 10 nor alternator i2 is running sothat no output voltage is produced across leads Tl, T2 and no outputvoltage is produced across leads 2Tl and 2T2, relay IFA2 and relay 2FA2will both be released since the winding of relay IFA2 is connectedacross leads TI and T2, and the winding of relay 2FA2 is connectedacross leads ZTI and 2T2. In this case an energizing circuit for relayIFAD is completed through contact 6 of relay 2FA2 and contact 4 of relayIFAZ, and an energizing circuit for relay ZFAD is completed throughcontact 5 of relay IFAZ and contact 4 of relay 2F'A2. Relays IFAD andZFAD will, therefore, operate to cause the energization of the alarmcircuit 63. In this case an alarm 64 will also be energized undercontrol of relay 2FA. Relay ZFA will release due to no voltage acrossthe load line Ll, L2 to cause it to close its contact 4, therebyconnecting ground to alarm circuit 54 to complete an energizing circuitfrom negative battery for the alarm circuit 64.

This application discloses but does not claim subject-matter that isdisclosed and claimed in our application serial No. 304,317, filedAugust 14, 1952.

What is claimed is:

1. In an electrical generating system having two engine-driven generatorunits, a load circuit, a transfer switch for connecting either of saidgenerators to said load circuit, a cam switch system having first andsecond pairs of normally open contacts successively closed duringalternate time intervals, and first and second relay systemssuccessively energized by the closures of said first and second pairs ofcontacts to respectively shut down one of said units, to start the otherof said units and to energize said transfer switch 9 to transfer theload circuit from the one of said generators to the other of saidgenerators.

2. In combination, a first and a second enginedriven generator unit foralternately supplying current to a load during successive predeterminedtime periods, a transfer switch responsive to the energization thereoffor transferring said load from one of said generator units to theother, means operative in response to a predetermined elapsed timeinterval following the starting of said first generator unit and whilesaid first generator unit is supplying current to said load for startingsaid second generator unit, means responsive to a predetermined voltagegenerated by said second generator unit for causing the operation ofsaid transfer switch to cause it to transfer the load from said firstgenerator unit to said second generator unit and means for stopping saidfirst generator unit after the transfer of said load to said secondgenerator unit.

3. In combination, a first and a second enginedriven generator fornormally alternately supplying current to a load during successivepredetermined. time periods, a transfer switch responsive to theenergization thereof for transferring said load from one of saidgenerators to the other, means for normally starting said secondengine-driven generator while said first engine-driven generator isrunning and supplying current to the load, means operated after apredetermined delay period following the time at which said secondengine-driven generator generates a certain output voltage forenergizing said transfer switch and means operated in response tofailure of said first engine-driven generator to supply current to saidload for starting said second engine-driven generator and for en--ergizing said transfer switch after a delay period which is smallrelative to said predetermined dclay period following the time at whichsaid second engine-driven generator generates a certain output voltage.

1. In combination, a first and a second engine driven generator fornormally alternately supplying current to a load during successivepredetermined time periods, a transfer switch responsive to theenergization thereof for transferring said load from one of saidgenerators to the other, means for normally starting said secondenginedriven generator while said first engine-driven generator isrunning and supplying current to the load, means operative under anabnormal condition for starting said second engine-driven generator inresponse to failure of said first enginedriven generator to supplycurrent to the load, timing means having a first circuit closing meanswhich is closed after a first predetermined operat ing period of saidtiming means and having a second circuit closing means which is closedafter a second predetermined operating period of said timing means lessthan said first operating period, means responsive to a certain outputvoltage of said second engine-driven generator for initiating theoperation of said timing means, means responsive to the closure of saidfirst circuit closing means for causing the energization of saidtransfer switch when said first engine-driven generator is supplyingcurrent to the load under a normal e1 t is to the other generator, meansfor starting econd generator While said first generator supplyingcurrent to the load, means re ponsive to a first predetermined voltagegen :1 by second generator for causing the eration of said transfermeans to cause it to transfer the load from said first generator to saidsecond generator, means for normally stopping said first engine-drivengenerator after said sec ond generator is supplying current to the loadand for preventing the stopping of said first enginedriven generatorunder an abnormal condition when the voltage generated by said secondgenerator drops to a second predetermined voltage less than said firstpredetermined voltage substantially at the time that said load istransferred to said second generator.

6. In combination, a first and a second enginedriven generator foralternately supplying current to a load during normal operation, atransfer switch for transferring the load from one of said enerators tothe other generator, a timing means having a first and a second circuitclosing means, means for closing said first circuit closing means andmeans for closing said second circuit closing means subsequent to theclosing of said first circult closing means, means responsive jointly tothe closing of said first circuit closing means and to a predeterminedvoltage generated by said second generator for causing the operation ofsaid transfer switch to transfer said load from said first generator tosaid second generator and means responsive jointly to the closing ofsaid second circuit closing means and to a predetermined voltagegenerated by said second generator for stopping said first engine-drivengenerator.

VINCENT T. CALLAHAN. LLOYD D. FRY.

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